The present invention is directed generally to cooling of an appliance, and more particularly, to heat sinks and a semiconductor cooling device using the heat sinks suitable for cooling semiconductor chips having a high heat dissipating density or semiconductor packages.
Disclosed in, e.g., Japanese Patent Unexamined Publication No. 60-134451 is a method of flowing cooling fluids to heat sinks attached to a multiplicity of integrated circuit chips mounted on a multi-layered printed board. An arrangement of this conventional technique is that the heat sinks are composed of tabular fins vertically attached to surfaces of the integrated circuit chips in parallel to a direction in which the integrated circuits are arrayed, the cooling fluids also flow in parallel to the fins in the array direction of the integrated circuit chips. Based on a structure disclosed in U.S. Pat. No. 4,686,606, the heat sinks consisting of the tabular fins perpendicular to the chip surfaces are mounted on the integrated circuit chips, and two bellows tubes each assuming an elliptical configuration in section to cause the cooling fluids to flow in and out of the heat sinks.
In any conventional techniques described above, the cooling fluids run in parallel to the surfaces of the integrated circuit chips. In contrast, according to a structure disclosed in U.S. Pat. No. 4,682,651, the tabular fins are radially mounted on heat dissipating elements, and the cooling fluids are made to flow in a radial direction from the central parts thereof.
Japanese Patent Unexamined Publication No. 62-119947 discloses a structure for cooling integrated circuit elements by means of a heat sink which is provided inside a bellows-type flexible structure and which has a plurality of concentric circular projections provided on a heat transfer surface and a nozzle which blows a refrigerant onto the center of the heat transfer surface.
There arise, however, the following problems inherent in the prior arts. In the technique disclosed in Japanese Patent Unexamined Publication No. 60-134451, the cooling fluids flow in such a direction that a multiplicity of integrated circuit chips are arranged on the board, and hence a temperature of the cooling fluid gradually rises. As a result, the chips disposed backwards encounter deterioration in cooling efficiency. This problem becomes serious, if a heat dissipating density further increases with a higher integration of the integrated circuits.
Steering clear of this problem entails such an arrangement that the integrated circuit chips are, as disclosed in U.S. Pat. No. 4,686,606, mounted with the heat sinks each provided with a bellows for permitting an inflow and outflow of the cooling fluid. According to this prior art, the fins which are provided inside the heat sink and which is vertically attached to the integrated circuit chip surfaces assume parallel tabular configurations, with the result that the flows of the fluid are made uniform. For this reason, there are employed flat bellows each taking an elliptical shape in section. This structure is superior in the cooling effect but suffers the following problem in regard to strength and reliability. A problem peculiar to the elliptical bellows lies in such a point that the bellows is easy to deform in a direction of a minor axis but hard to deform in a direction of a major axis. This property makes it difficult to absorb the thermal deformation in the major axis direction and brings about a possibility that excessive stress acts on the integrated circuit chips. This problem is derived from the fact that the fins assume the parallel tabular configurations, and the cooling fluids are made to flow from one ends of the heat sinks to the other ends thereof in parallel to the surfaces of the integrated circuit chips.
While on the other hand, according to U.S. Pat. No. 4,682,651, although a heat transmissibility from the fins to the cooling fluids typically becomes larger as gaps between the parallel tabular fins become narrower, it is impossible to keep the minute gaps because of the gaps opening in the radial directions in the radially arranged fins, resulting in a drop in the heat transmissibility. This conventional technique adopts the arrangement that the fins stand directly on the surfaces of the heat dissipating elements, and hence the mounting areas thereof are conditioned by the heat dissipating elements. Those fins are restricted in terms of enlargement of the heat transfer area. Besides, if the fins are thinned to enlarge the transfer areas, the fin efficiency decreases. It is eventually difficult to increase a radiating performance well over a certain degree.
The art shown in Japanese Patent Unexamined Publication No. 62-119947 mentioned before employs a bellows having a circular cross-section which allows an easy deflection in all directions. This art, therefore, is free from the problem concerning the strength and reliability encountered with the known art which employs elliptical bellows. The heat transfer mechanism provided on the bottom of the bellows basically relies upon heat transfer provided by impinging jet flow and incorporates concentric annular projections which produce turbulency thereby contributing to promotion of the heat transfer.
The heat transfer promotion effect produced by the annular projections, however, is appreciable only when the height of the projection is not so high, more specifically only when the height to width ratio is near 1.0. Namely, an unduly large height of the projection impedes the flow of the cooling medium thereby suppressing the heat transfer. The art disclosed in Japanese Patent Unexamined Publication No. 62-119947, therefore, is restricted in terms of increase in the heat transfer area and, hence, can provide only limited cooling performance.